This invention relates to an improvement of a method and apparatus for suppressing redundancy and encoding picture information of half tones and then transmitting the encoded information, and more particularly a method and apparatus for transmitting encoded picture information binarized by a dither method.
In recent years, the dither method has been frequenty used for converting an analog picture signal containing picture information of a half tones into a binary code. According to this method, at the time of binarizing an analog signal containing a half tone component, a binarizing judging threshold value is varied by using a random function or a quasi random function for generating bright spots of a number corresponding to a local average value of an input picture signal. For example, a picture image is converted into a block at each M picture element points.times.N scanning points (M and N are positive integers) and different binarizing judging levels are assigned for respective picture elements of each block so as to binarize the analog picture signal according to the binarizing judging levels, whereby bright spots are systematically arranged in the picture element space, thus reproducing the half tone of the picture image.
Generally, for the purpose of decreasing the quantity of information, when transmitting a picture image, the binarized picture signal is encoded with its redundancy being suppressed. A picture signal binarized by the dither method has also been encoded and then transmitted with Modified Huffman (MH) or Modified Read (MR) or Modified Modified Read (M.sup.2 R) based on CCITT T-6 encoding systems, for example.
However, a picture signal binarized by the dither method generally contains a large member of black and white variations. Therefore, when a binarized picture signal is encoded as it is with the MH, MR or M.sup.2 R encoding system, the quantity of information to be transmitted becomes enormous, thus requiring a long transmission time.